Temporarily rejected by greylisting
You do not need to change the email address immediately.
The receiving mail server temporarily rejected the first attempt to help filter spam. A normal sending server retries automatically after a delay.
What to do now
- Wait a while, then check the sending result again.
- If you operate the mail server, check the queue for an automatic retry.
- If it persists for a long time, inspect sending-server retry settings and receiving-server policy.
Representative reply
451 4.7.1 Greylisting; please retry later
Retry decision
A retry is likely to help. Allow the sending server’s normal automatic retry, then check the outcome. Acceptance is not guaranteed.
Why deliberately reject the first attempt?
Normal mail servers retry after a temporary SMTP error (4xx). Greylisting temporarily rejects an unfamiliar sending request once and waits for this retry. Some unwanted bulk-sending systems do not retry properly, so this behavior helps filter spam.
First attempt
- Sending server
- Receiving server
451 / Try again later- Wait for the sending server’s scheduled retry
Retry
- Sending server
- Receiving server
- The message may then be accepted
Typical stage
RCPT TO
- CONNECT
- EHLO
- MAIL FROM
- RCPT TO
- DATA
- DELIVERY
Stages vary by server. Confirm the actual stage from the complete reply and session logs.
What is SMTP Reply Code?Open only the explanations you need
Three-digit server reply: 4xx is transient, 5xx permanent. Read the complete text to investigate the cause.
What is Enhanced Status Code?Open only the explanations you need
An extended status such as 5.1.1. Server wording and usage may vary.
What is Greylisting?Open only the explanations you need
Temporarily defers unfamiliar mail and waits for a normal SMTP server retry.
Check directly
- Check that the SMTP reply is in the 4xx range.
- Check the complete reply for greylist, greylisting or postgrey.
- Wait a while, then check the sending result again.
- If you operate the mail server, check the queue for an automatic retry.
- If it persists for a long time, inspect sending-server retry settings and receiving-server policy.
Cautions
Observed DSNs do not map one-to-one to causes. The stage shown is typical; confirm it with the full reply and actual logs.
Similar reply wording and observed status codes
greylistgreylistingpostgrey
Observed DSNs: 4.7.1, 4.2.0, 4.5.0, 4.5.1